Transport/storage container for radioactive elements

ABSTRACT

A storage/transport container comprises a floor, a side wall, and a cover fittable with the side wall to form with the floor and side wall a closed interior having a height between an inner face of the floor and an inner face of the cover that is greater than an overall length of the element. A spring is engaged between a lower end of the rod and the floor and has a spring force smaller than a weight of the rod so that, when the cover is above the floor, an upper end of the rod is spaced below the cover and, when the floor is above the cover, the spring presses the rod upper end against the cover.

FIELD OF THE INVENTION

The present invention relates to a transport and/or storage container for radioactive elements. More particularly this invention concerns such a container used to ship fresh or used fuel rods or high-active-waste glass units.

BACKGROUND OF THE INVENTION

A typical storage/transport container for radioactive elements is basically formed as a massive barrel, typically of reinforced concrete, having a flat circular floor, a cylindrical side wall extending upward from the floor, and a flat circular cover that fits on the upper rim of the side wall so as to define a cylindrical interior. Since the elements placed in such a container can be of different lengths, since they expand and contract somewhat because of radioactive-decay heating, and also since the container is not made to extremely tight tolerances, it is standard to make the interior somewhat taller than the longest element that is likely to be stored in the container. This leaves under normal circumstances, that is when the container is standing on its floor with its cover up, an empty free space above the elements and below the cover.

The problem with this type of construction is that in the event of an accident when the container is dropped on its cover, breakage is likely. If, for instance, the container is dropped in such a manner that it is inverted with its floor up and its cover down, during the fall the elements inside it will naturally remain roughly in their starting position, that is engaging the floor and spaced from the cover. When, however, the container lands on its cover, the elements inside the container will travel and will, like massive hammers, strike the inside face of the cover with great force, transferring all their considerable kinetic energy to the cover. Thus the cover is struck from the inside, in a direction that is not really what it was designed to resist, so it can be popped off and the contents spilled.

OBJECTS OF THE INVENTION

It is therefore an object of the present invention to provide an improved transport/storage container for radioactive elements.

Another object is the provision of such an improved transport/storage container for radioactive elements which overcomes the above-given disadvantages, that is which can better resist breakage if it is dropped on its cover.

SUMMARY OF THE INVENTION

These objects are attained by a storage/transport container comprising a floor, a side wall, and a cover fittable with the side wall to form with the floor and side wall a closed interior having a height between an inner face of the floor and an inner face of the cover that is greater than an overall length of the element. According to the invention a spring is engaged between a lower end of the rod and the floor and has a spring force smaller than a weight of the rod so that when the cover is above the floor an upper end of the rod is spaced below the cover and when the floor is above the cover the spring presses the rod upper end against the cover.

Thus with this system, as the container is inverted so that its floor is above its cover, the load will be taken off the spring and the spring will shift the element toward the cover until it actually is pressed by the spring against the inner face of the cover. Thus if the container is inverted and dropped, by the time it hits the ground the element will be already in contact with the cover and will not strike it with a delayed hammer action likely to loosen the cover.

According to the invention the element is a fuel rod. In fact the container is designed to hold a plurality of the elements, each with its own spring so that elements of different length can be accommodated.

The spring in accordance with the invention is a simple coil compression spring. It can be at least partially received in a pocket formed in a lower end of the rod so that the system of this invention can be used with a conventional transport/storage container. Typically the pocket is deep enough to completely contain the spring in compressed condition so that, under normal circumstances, the element sits directly on the floor of the container. Each element is formed with such a pocket for its spring.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

FIG. 1 is a partial axial section through a container according to the invention as it is being loaded;

FIG. 2 is a view like FIG. 1 showing the loaded and closed container; and

FIG. 3 is a view like FIG. 2 but showing the container inverted.

SPECIFIC DESCRIPTION

As seen in FIGS. 1 and 2, a standard container according to the invention is centered on a normally vertical axis A and has a flat horizontal floor 3, a cylindrically tubular side wall 4, and, when complete, a flat horizontal cover 5 together defining a cylindrical interior 1 having a height H. Such a container is typically loaded with radioactive fuel elements, here spent fuel rods 2 of which one is shown. The rod 2 has an overall length h which is shorter than the height H by a distance f so that, when sitting on the floor 3, there is a space between its upper end and the cover 5 as shown in FIG. 2. The cover 5 here is shown as one piece although it is often constituted as two separate disks that may even be separated by a slight spacing.

According to the invention the lower end of the rod 2 is formed with a blind cylindrical pocket 7 in which is seated a steel coil-compression spring 6, although it is within the scope of the invention to use an elastomeric spring element. With high-active-waste glass elements the pocket 7 is of rounded cup-shaped. When unstressed, this spring 6 has an overall length L that is substantially more than the distance f. The strength of this spring 6 is, however, such that the weight of the rod 2 is sufficient to compress it by an amount V until it is completely contained in the pocket 7 and the rod 2 sits with its lower end directly on the floor 3. Thus as the rod 2 is lowered into the container, the spring 6 is prestressed.

With this system, if the container is inverted as shown in FIG. 3, the spring 6 will extend and will shift the rod 2 downward through the distance f such that what is normally its upper end bears against the inside normally lower face of the cover 5. Thus if the container is inverted and dropped, by the time the cover 5 and rim of the side wall 4 strike the ground, the rod 2 will already be in solid contact with the inner face of the cover 4 and it will not act like a delayed hammer on this inner face. Instead the cover 5 will merely be subjected to compression and is not likely to be knocked off the side wall 4. 

1. In combination with a radioactive element, a storage/transport container comprising: a floor; a side wall; a cover fittable with the side wall to form with the floor and side wall a closed interior having a height between an inner face of the floor and an inner face of the cover, the element having an overall length shorter by an amount shorter than the height; and a spring engaged between a lower end of the rod and the 11 floor and having a spring force smaller than a weight of the rod, whereby when the cover is above the floor an upper end of the rod is spaced below the cover and when the floor is above the cover the spring presses the rod upper end against the cover.
 2. The storage/transport container defined in claim 1 wherein the element is a fuel rod.
 3. The storage/transport container defined in claim 1 wherein the spring is a coil compression spring.
 4. The storage/transport container defined in claim 3 wherein the rod is formed at its lower end with a pocket at least partially receiving the spring.
 5. The storage/transport container defined in claim 4 wherein the pocket is deep enough to completely contain the spring in compressed condition. 